网络数据下载

@interface ViewController ()<NSURLSessionDataDelegate,NSURLSessionDownloadDelegate>
// 显示图片
@property (weak, nonatomic) IBOutlet UIImageView *imageView;

// 显示进度
@property (weak, nonatomic) IBOutlet UIProgressView *progressView;

// 下载任务的属性
@property (nonatomic, strong) NSURLSessionDownloadTask *task;

// 网络请求类
@property (nonatomic, strong) NSURLSession *session;

// 发送请求类
@property (nonatomic, strong) NSURLRequest *request;

// 用来保存已经下载的数据,供继续下载使用
@property (nonatomic, strong) NSMutableData *data;

@end

@implementation ViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view, typically from a nib.
    // 设置progressView开始值
    self.progressView.progress = 0;
    
}

#pragma mark - 开始下载
- (IBAction)startDownload:(id)sender {
    
    // 下载的url
    NSString *urlStr = @"http://hc24.aipai.com/user/396/23170396/4799208/card/25053445/card.mp4?l=a";
    NSURL *url = [NSURL URLWithString:urlStr];
    
    // 初始化请求类
    self.request = [NSURLRequest requestWithURL:url];
    
    // 创建NSURLSession
    
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    
    self.session = [NSURLSession sessionWithConfiguration:configuration delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    // 下载请求任务
    self.task = [self.session downloadTaskWithRequest:self.request];
    
    // 开启
    [self.task resume];
    
}

#pragma mark - 暂停
- (IBAction)pauseDownload:(id)sender {
    
    // 暂停
    if (self.task) {
        // 暂停并保存之前已经下载的内容
        
        __weak typeof (self)weakSelf = self;
        [self.task cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
            weakSelf.data = [NSMutableData dataWithData:resumeData];
        }];
    }
    
    // 暂停任务
    [self.task suspend];
}

#pragma mark - 继续下载
- (IBAction)continueDownload:(id)sender {
    
    // 判断当前任务是否有,是发送请求还是处理数据
    if (self.task != nil) {
        // 说明已经下载,这里要处理的就是数据
        self.task = [self.session downloadTaskWithResumeData:self.data];
    } else {
        // 此时没有下载任何内容,应该重新发送请求下载
        self.task = [self.session downloadTaskWithRequest:self.request];
    
    }
    
    // 启动任务
    [self.task resume];
}

#pragma mark - 代理方法
// 下载完成走的方法
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    // 找到文件夹管理器
    
    NSFileManager * fileManager = [NSFileManager defaultManager];
    // 先找到沙盒
    NSArray *urlArray = [fileManager URLsForDirectory:NSDocumentDirectory inDomains:NSUserDomainMask];
    NSLog(@"%@", urlArray);
    // 根据沙盒路径获取Document路径
    NSURL *url = [urlArray objectAtIndex:0];
    NSLog(@"%@", url);
    // 根据系统推荐的类型去保存下载的url
    NSURL *saveUrl = [url URLByAppendingPathComponent:downloadTask.response.suggestedFilename];
    NSLog(@"%@", saveUrl);
    // 使用
    self.imageView.image = [UIImage imageWithData:[NSData dataWithContentsOfURL:saveUrl]];
    
}

- (void)URLSession:(NSURLSession *)session downloadTask:(nonnull NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    // 下载当前段的数据
    NSLog(@"bytesWritten = %lld", bytesWritten);
    // 已经下载的总数据量
    NSLog(@"totalBytesWritten = %lld", totalBytesWritten);
    // 表示总进度
    NSLog(@"totalBytesExpectedToWrite = %lld", totalBytesExpectedToWrite);
    // 设置progressView的进度值
    self.progressView.progress = (CGFloat)totalBytesWritten / (CGFloat)totalBytesExpectedToWrite;
}

- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}